Fast counting circuit



Apl'll 28, 1953 M. J. JAKOBSON 2,636,993

FAST COUNTING CIRCUIT Filed Nov. '7, 1951 34 scALER .3/ DISTRIBUTEDDISTRIBUTED AMPLIFIER OOINGIDENGE 327 7 scALER STRIBUTED 27 29 AMFLIFIER7 7 V b DISTRIBUTED DELAY DISTRIBUTED GATE 213 COINGIDENOE LINEAMPLIFIER GENERATOR 9 ODISTRIBUTEDO J AMPLIFIER Z6 m w A '3 20 g AINVENTOR. TIME 2f MARK I1 JAKOBSON fiw/d/fin Patented Apr. 28, 1953UNITED STATES PATENT @PFICE 6 Glaims. (@l. 250-71) I The presentinvention relates to an improved electronic circuit particularly adaptedfor highspeed counting and coincidence counting.

Modern research in the field of physics has emphasized the need forcircuits capable of counting rapidly recurring pulses and apparatuscapable of producing such pulses from high-speed particles. Also thereis a need for equipment capable of identifying particular particles inthe presence of other particles having similar oharacteristics. Forexample, the detection and counting of mesons is particularly diflicultin that other charged particles, inevitably present, produce backgroundsignals of such magnitude that the desired signal is almost entirelymasked. Conventionally mesons are identified and counted by measuringthe (3 rays produced by meson decay. Numerous difiiculties anddisadvantages attend this method and thus the present invention isdisclosed in connection with the counting of socalled 1r mesons;however, it will be appreciated thatthe invention is not so limited andmay be in fact employed to count various other particles with propercircuit modification.

It is an object of the present invention to provide an improvedhigh-speed counting circuit.

It is another object of the present invention to provide an improvedcoincidence counting circuit.

It is a further object of the present invention to provide an improvedelectronic counter having double coincidence circuits for identifyingparticular pulses in the presence of high back round noise.

It is a still further object of the present invention to provide animproved counter for 17+ mesons.

Numerous other advantages and objects of the present invention willbecome apparent from the following specification and claims takentogether with the accompanying drawing wherein Figure 1 is a blockcircuit diagram of one embodiment of the present invention and Figure 2is a series of graphs having a common time base and showing thewaveshapes of signals at various points in the circuit of Figure 1.

With regard to the counting of mesons, it is noted that the existence ofthese unstable particles has only within recent years been confirmed andmuch of the theory relative thereto is still in the formative stage. Ithas been determined that there are positively and negatively chargedmesons and also mesons have been further classified as heavy and lightmesons. The heavy mesons, called 1r mesons, have a mass of about 284times that of an electron and decay into a mesons (light mesons) havinga mass of about 216 times the mass of an electron. Also ,u mesons decay,and in vacuum this decay may result in the liberation of ,8 rays. Thehalf-life of 11' and a mesons is measured in millionths of a second andthus it will be seen that it is particularly difficult to detect orcount these particles. Furthermore, the decay products of TI and amesons depend upon the original charge of the particles, which may beeither plus or minus, and because of this it has been the practice toidentify mesons by the measurement of the resultant [3 rays produced.The illustrated embodiment of the present invention accomplishes themeasurement of 7+ mesons directly and by a novel combination of fastelectronic circ its reduces the accidental background at the counter toa few percent of the total count.

Considering now the illustrated embodiment of the invention e ndreferring to the drawing, there is shown in Fig. l a photon beam M asfrom a high energy particle accelerator, .such as a synchrotron. it hasbeen determined that the incidence of a high energy beam of particlesupon certain substances produces mesons and there is provided in thepath of beam H a polyethylene cube 52 for this purpose. A beam of mesonsi3 is emitted from cube 62 as a result of the incident photon beam 2 land these mesons are of the heavy type with a positive charge, and thusdesignated for convenience .-r+ mesons.

It has been determined that the mesons produced in cube it are emitteddirectionally therefrom; the direction being dependent upon a variety offactors. In the illustrated embodiment a high concentration of mesonsare emitted at right angles to the incident photon beam; however, whenthe so-called beam of mesons are emitted from the back of cube l2 andtravel in the same direction as photon beam ll, it is desirable todirect the meson beam away from its original course as by a magneticfield in order to reduce the amount of extraneous charged particlespresent in the meson beam and to thereby reduce the background signal inthe counter.

In the path of the highly concentrated meson radiation, or beam as itwill hereafter be called, there is aligned a pair of scintillationcrystals it and l It desired that the 1r mesons decay in the secondcrystal to mesons, as it is in conjunction wit phenomenon that theillustrated counting device operates. lnorder to s'topmesons in crystalit it is necessary crystal it be situated the proper distance from cube#2 so that the 1r+ mesons will lose their kinetic energy at this point.Although mesons have a relatively short range even in vacuum, it ispreferable to slow down the 1r me on beam between cube l2 and thecrystals in order that crystals l4 and I6 may be positioned quite closeto cube [2. This may be accom lished by providing an absorber I! in thepath of vr+ meson beam I3 intermediate cube !2 and crystal It; thepurpose of absorber ll being to slow down the w mesons so that they willreach the end of their path in crystal I6. In this respect, it is notedthat a variety of absorbing or retarding materials may be employed andfur ther, that it is necessary to have a monoenergetic 1r+ meson beamfor substantially all ofthe 7r mesons to stop in crystal 1.6.

Although it is not necessaryit is advantageous to combine crystals l4and I6 and absorber 4'1 a telescope arrangement l8 including atube issurrounding and supporting same and providing not only a convenientsupport structure but-alsoacting to shield crystals Myand IE fromextraneous ad ation E this purpose. be [5 may be form d. of asocdisieldin material, su h as ead or he ike! Attached tcc ysta 4 and I are phcmu1til er t bes 2| and. r sp cti ly. and pr fe abl there is formeda,light-tightconnection between crystals l4 and Hi" andphotcmultipliertubes 2| and 22, andin order to further intensify-the light pulses tophotomultiplier'tubes 2 and-2 3, crystals Miand lfifmay be individuallyenclosed with a 118- fleeting surface; such as aluminum foil. It is-advantageous to directly attach crystalsl4 and IG to photornultipliertubes 21- and 22, respectively, and to this end apertures n aybeforrnedin tube i9fand the crystals joined to thecathodesoi therespective photomultiplier. tubes at these apertures, as shown; lighttight connectionbeinginsured by wrapping the connection with black tapeor the like. 7 Y' There is provided a, pair of amplifier circuits 23;and 24 connected to theoutputs-of photomultiplier tubes 2! and- 22;respectively/and the output of amplifiers ?and-fibre connected tocoincidence circuit 28'. Amplifiers-'23 and 24 and coincidencecircuittfiarepiejieesuy of the distributeditype in order that-rapidity-or responsewill be: maximised.- Distributedamplifiers are knownin the artandreference-is made to U. S. Patent No. 2,593,948, issued April 22, 1952,to Wie' gaiid et al. for-a disclosure or distributed coincidencecircuits. With these types 'ofcircuits, it 0 is'pos's iblet'e obtainresponses in IX IO 'seconds which will be seentobeamaterial advantage inthe-illustrated application of the-invention.

' Coincidence circuit'Z'G operates to passa signal whenthe two incomingsignals are in timesc'oine cid'ence and this output signalis delayed apredetermined amount byfiaoelay network which may constitute a delaycable or linefl' connected to coincidence circuit 26.. The delayedsignal may be further amplifiedby: a distributed ampli-x fier 28connected-to delay cable ZIand' isthen applied to' a gategeneratorcircuit 29; the opera.- tion of'these circuit-elements being-consid'eredin more detail below; 'Gate generator ZS-produces squarewave pulses of predetermined duration-and of 'equarma'gnitude andtheseare applied to second distributed coincidence circuit '31 and; maybe counted by a sealer circuita32gconnected'intermediate gate generator29 and coincidence: circuit3l. l

In addition to he. above-no ed l ents a connections, there. .5 "provideda further connec-z tion from photomultiplier tube 22 of second crystal16 to the e ndcoin dence circuit 3!, and a distrib ted. amplifier-.3.3..may be. inserted in this connection. A second sealer circuit 34 isconnected to the output of second coincidence circuit 3| to record thesignals therefrom and an output terminal may also be provided at thispoint for the connection thereto of various other measuring devicespossibly advantageously associated with the above-described circuit.

Considering now the operation oft-h present invention and referring inpart to Fig. 2, it is first noted that a telescope I8 is disposed toenclose a plurality of mesons moving longitudinally of the telescope isand designated as a beam l3. One method of obtaining a relatively strongmeson beam I3 is to bombard a cube I: of polyethylene with abeam ofphotons I I which with certain geometryproduces a beam of mesons [3 atright angles to the incident photon l i as illustrated. Within telescopeHi there is situated. a pair of scintillation crystals M and IE, formedof stilbene for example, and aligned with meson beam l3 so that beam l3first passes crystal I l and then into crystal it; Also within telescopei8'there may be provided an absorber I! which is preferably disposedadjacent cube it" and which functions to reduce the energy ofmeson beamHand to therefore limit its range. The range of meson beam is reduced tothe point where mesons of a predetermined energy come to rest in secondcrystal. i5, and it is these mesons that are counted. If a substantiallymoncenergctic beam ofmesons is to be counted, then an absorber ll ofproper material and thickness will stop practically all of the mesons incrystal Iii; however, in the circumstance that mesons of variousenergies are present an absorber having a variable total thickness isbest employed in order that mesons ofjdiiferent energies may besuccessively stopped in crystal i6 and counted.

Mesons passing through scintillation crystal [4 create individual lightpulses which are transmitted to photomultiplier tube 2! and thereinconverted to corresponding electrical signals or pulses. Considering asingle meson passing through. crystal l4, there is shown at Fig. 2(a) avoltage pulse produced by photomultiplier tube 2| as a'consequencethereof. This meson also produces a light pulse upon striking secondcrystal l6 which is in turn converted into an electrical signal byphotomultiplier tube 22. Assuming that'absorber I 7 has removed from thesigle sample meson suificient energy so that the meson comes to rest insecond crystal It, there is produced in second crystal IE- a secondsomewhat weaker light pulse by the decay of the incident w meson to a Mmeson. The light pulse produced by the meson is somewhat Weaker thanthat from the incident 1r+ meson, as may be seen at Fig. 2(b) The twosignals produced by 1+ meson, one. in each crystal, are substantiallycoincident in time and thus they are passed by first coincidence circuit2t, and the resulting signal is shown at Fig. 2(a). It will be notedthatthe pulse produced by the meson in crystal I6, lags in time the H mesonsignals and as there is no signal corresponding in time to the mesonpulse, it does not pass the coincidence circuit. Inasmuch as the,illustrated embodimentof theinvention isdesigned to count 1r+ mesonswith maximum accuracy, it is necessary to minimize the possibility thatother charged particles will be counted. To this end the presentinvention, provides for a coincidence between the signal fromtheincident+ mesons and their ,LL+ meson decay products 'andaccomplishessuch bydelaying the. o

meson signal. The signal from. first: coincidence circ'uitlit'is fedthrough. delay: cable 2.? which. has

a known impedance per unit length and a predetermined length tointroduce a calculated delay the'arri-val of the signal from firstcoincidence circuit til-to gate generator 29. The lengthofthedelayintervai is made sufliciently longsothat theresulting gatesignal willcoinmeson signal, as further-explained below.

Gate generator Elloperatesto produce a square wave pulse of knownduration when triggered-by an'incomingsigna'l, such as thatfrom firstcoincidencecircuit' 26-, andthe square wave preferablyhas'a very shortrisetime; Also gate generator 2'9. is, preferablycontrollable to producea square wave. gate signal or" any desired duration with a. desiredrange. The gate signal shown at Fig. 2(a) is applied to one inputterminal of sec ond coincidence circuit ti 'and'there is applied totheother-input circuitthereof the amplified signal from photomultipliertube. 22 connected to second crystal it. This photomultiplier tubesignalincludes the l+ meson signal as noted above and, inasmuch as the1r+ meson signal producing the. gate signal has. been delayed the properamount, there is thus produced a coincidence at second coincidencecircu-i-t'Ei and an output signal..(Fig. 2(f)) is generated, which mayberecordedon. sealer circuit Stand also applied to other'measuring. means,as. desired, through terminalzdfi. Also the number of gate signalsgenerated may be recorded by sealer circuit 32 connected between gategenerator and second coincidence circuit 3!.

From the above it will be seen that the coincidences betweengatesignalsand meson signals are recorded as a measure of the number ofrest in second crystal Hi. It will beappreciated that accurate countingwith the illustrated embodiment of the invention requires a minimizationof accidental coincidences in the circuit and maximization of M anddelayed 1r+ coincidences. In order to fulfill these requirements, it isbest that the gate signal be delayed a maximum amount and yet includethe meson signal. This is accomplished by delaying the 1r signal as muchas possible, i. e., a time about equal to the mean life of 1r mesons andby making the gate signal rise time very short. By this means broadpulses produced at the same time as the 1r meson signals, by protons forexample, will not extend past the beginning of the gate signal and causeundesirable coincidences. Also the gate signal is made to have anappreciable duration so that the probability of a coincidence with the/.L+ meson signal is maximized.

As an example of preferred operating conditions the delay introduced maybe about 2.5 1()- seconds and the gate signal may have a rise time of.005 microsecond and a duration of .08 microsecond. With theseconditions the gate signal extends over about three 1r meson half-livesand thus about 95% of the 113* mesons are counted. It is necessary forgate circuit 29 to discriminate and to thereby reject signals of lessthan a predetermined minimum magnitude in order that the accidentalbackground count will be minimized, and thus care must be taken withconventional gate circuits, in that operation thereof with less than acertain minimum gate signal duration commonly destroys thediscriminatoryproperties thereof.

As will be: apparent tothose skille'drin the art. the present inventionexhibits advantages over prior known meson counting techniques. Forexample, the detection of 1r+ meson decay has the advantage overconventional 14+ meson decay detection of reducing the accidentalbackground; such reduction being essentially given by the ratio of 11-meson mean life FT/211+ to the ,c meson mean life m,.+. This ratio'rm.+/m,.+-0 .01 theoretically, and while this theoretical reduction isnot quite obtainable because of electronic limitations, there is amaterial reduction of background signals. A further advantage lies inthefact that in counting 1r+ mesons no corrections are necessary for cmesons or H- meson pair production, which ordinarily present quite, aproblem.

It is possible to further decrease the background by using a tripledelayed coincidence involving vr' -afi decay; however, the countingefiiciency is quite low and thus the applicability thereof is somewhatlimited. Also the above-described apparatus-may be employed to determinethe 1+ meson half-life and mean-life by employing a variable delaynetwork or cable 2? and results are obtainable to within 0.002microsecond.

While the present invention has been disclosed with respect to 2. singleembodiment it will be apparent to those skilled in the art that variousmodifications may be made, within the spirit and scope of the inventionand thus it is not intended to limit the invention except by the termsof the following claims.

i i hat is claimed is:

1. An improved electronic counter comprising a pair of scintillationcrystals aligned in the path of a beam of particles to be counted, apair. of photomultiplier tubes connected one to each of saidscintillation crystals to produce electric sisnals from li ht pulses insaid crystals, a first coincidence circuit connected to the output ofsaid photomultiplier tubes and passing a signal upon the coincidence oftwo input signals, a gate generator connected to said coincidencecircuit and producing a square wave voltage pulse when triggered by theoutput of said first coincidence circuit, a second coincidence circuitconnected to said gate generator, electrical connection from thephotomultiplier connected to said scintallation crystal disposed in thedirection of travel of said beam of particles from the other of saidscintillation crystals to said second coincidence circuit, meansrecording the output of said second coincidence circuit, and electronicdelay means delaying the signal from said first coincidence circuit anamount or" time substantially equal to the decay time of the particlesto be counted in said second crystal, whereby only signals fromparticles to be counted trigger said second coincidence circuit.

2. An improved electronic counter as claimed in claim 1 further definedby an absorber disposed in the path of said beam of particles to reducethe energy of the particles and cause particles of a particular energyto decay in said scintillation crystal and to thereby be counted by saidsealer circuit.

3. An improved meson counter comprising a first scintillation crystaldisposed in a meson beam, a photomultiplier tube connected to said firstscintillation crystal, a second scintillation crystal disposed in saidmeson beam in the direction of travel thereof from said first crystal, a

photomultiplier tube connected to said second scintillation crystal, afirst coincidence circuit having an input connected to saidphotomultiplier tubes, a delay line connected to the output of saidfirst coincidence circuit and delaying the pulses therefromapproximately .025 microsecond, a gate generator circuit having an inputconnected to said delay line, a second coincidence circuit having aninput connected to said gate generator circuit, connection between thephoto multiplier tube of said second scintillation crystal to the inputof said second coincidence circuit, and recording means connected to theoutput of said second coincidence circuit and recording the number ofmesons decaying in said second scintillation crystal and producingsignals coincident with delayed signals from said first coinci dencecircuit.

4. An improved meson counter as claimed in claim 3 further defined bysaid gate generator circuit producing a square Wave voltage pulse havinga duration of approximately the three times the meson half -life.

5. An improved meson counter as claimed in claim 3 further defined by anabsorber disposed in the path of said meson beam in front of saidscintillation crystals relative to said meson beam and reducing theenergy of mesons passing therethrough to cause mesons of a particularenergy to come to rest in said second. scintillation crystal and decaytherein to be counted.

6. .An improved meson counter for counting 1r mesons and comprising atelescope aligned with and surrounding a meson beam to b counted, firstand second scintillation crystals disposed in said telescope with saidsecond crystal being displaced from said first crystal in the directionof travel of said beam, an absorber disposed said telescope on theopposite side of said first crystal from said second crystal andreducing the energy of mesons passing therethrough a predeterminedamount to cause mesons of a particular energy to come to rest in saidsecond crystal,

first and second photomultiplier tubes connected to said first andsecond scintillation crystals respectively, a first distributedcoincidence circuit having an input connected to said first and secondphotomultiplier tubes and producing an output pulse for each coincidenceof input signals, a delay cable connected to said first coincidencecircuit and delaying the signal therefrom an amount substantially equalto the half-life of 1r" mesons, a gate generator connected to said delayline and triggered by the signal therefrom to produce a square Wavevoltage pulse having a fast rise time and a duration of substantiallythree 1r meson half-dives, a second distributed coincidence circuithaving an input connected to said gate generator, connections from saidphotomultiplier tube to said second coincidence circuit to transmitthereto voltage pulses resulting from t meson decay products of 1rmesons coming to rest in said second scintillation crystal, andrecording means associated with said second coincidence circuit countingcoincidences between ,LL+ meson signals and said delayed gate signal asa measure of 17 mesons coming to rest in said secondscintillation'crystal.

MARK J. JAKOBSON.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,517,404 Morton Aug. 1, 1950 2,554,933 Wou'ters May 29, 19512,593,948 Wiegand et a1 Apr. 22, 1952 2,595,552 Thomas May 6, 1952 OTHERREFERENCES Introduction to Modern Physics, Richtmyer et al., 1947, pub.by li icGraW-Hill Book Co., New York, N. Y.

A Fast Coincidence Circuit, etc., Bell et al., MDDC-799, April 27, 1947,pp. 1-4.

